Though Arc'teryx named it after a radioactive element with a half life of 10. 45 million years, the Women's Thorium AR Hooded Down Jacket isn't, thank goodness, radioactive however, it does slow your decay in cold weather to give you an outdoor half life longer than 10. 45 seconds. Crafted with a combination of 750 fill European goose down and selectively situated synthetic insulation, this jacket keeps you warm whether you wear it on its lonesome during your chilly backpacking trips or under a hardshell whilst perusing some secret powder stashes. Down is a mix of feathers and clusters that work cooperatively to create insulating air pockets, trapping warmth and preventing cold air from passing. The Thorium's synthetic insulation works the same way, creating an air pocket barricade, but with one substantial difference: wet down is dead down, which means you'll go down quickly from the cold. By utilizing synthetic insulation in strategically placed inserts, this jacket is inherently water resistant and dries quickly when wet. So it's no surprise that Arc'teryx placed the synthetic insulation in areas which bear the brunt of exposure to moisture the shoulders, hood, and neck gaiter area. Technical bells and whistles are fun, but when it's all said and done, you want a down jacket that will handle the rigors of daily abuse precisely why Arc'teryx opts for ripstop Colibri with a DWR treatment as the face fabric. So whether you hike year round, ski in and out of bounds, or schlep from the dorm to class on inclement days when your fellow classmates bury themselves in bed, the Thorium AR hoodie is there.